Differences in the distribution of catecholamine varicosities in cat and rat reticular formation.

The distribution of catecholamine varicosities within the brainstem reticular formation of the immature cat was determined by means of the formaldehyde-induced fluorescence technique. A continuous pattern of intense, green, medium-sized varicosities exists at nearly all brainstem levels. At most of these levels the varicosities appear within the boundaries of reticular formation nuclei. However, in rostral mesencephalon, some of the varicosities of the pattern lie in proximity to perikarya of the red nucleus. In addition, numerous varicosities in caudal medulla appear to extend from the pattern into nonreticular formation nuclei. A comparable pattern of reticular formation fluorescence is absent in the rat and this finding is believed to represent a true interspecies difference.